The present invention relates to an extraction method and extraction apparatus for cleaning soil, particularly soil which is contaminated with hydrocarbons and/or hetero-organic compounds.
In extraction methods of this type contaminated soil is treated with a solvent in an extractor, the solvent laden with the contaminating materials or pollutants is removed from the soil and separated into a contaminant containing extract and a reusable solvent.
A known process of this type is described on pages 576 and 577 (FIG. 1) in the article "Extraction as a Method for Cleaning Contaminated Soil: Possibilities, Problems and Research" in Management of Uncontrolled Hazardous Waste Sites, published by Hazardous Materials Control Research Institute, Silver Spring, Md., USA, 1984. No concrete solutions to the problem of cleaning contaminated soil are provided in this reference, although general and theoretical considerations are discussed.
An extraction method for solids is disclosed in "Ullmanns Encyclopedia of Chemical Technology, Volume 2, pp. 722 to 729, however these methods deal exclusively with extractions of oil seeds, drugs, bones, absorbing clay, catalysts and beet sugar. A belt filter (FIG. 11, p.728) and plane cell-rotating filter (FIG. 10, p. 728) are described in this reference. A method of cleaning contaminated earth or soil is not disclosed in this reference.
A single and multistage countercurrent rotating drum extraction method are described in U.S. Pat. No. 4,098,648 and German Published Patent Application DE-OS 37 26 282, in which the contaminated soil is washed by a solvent, such as hexane and pentane. The method disclosed in these references requires a costly drying of the soil with an expensive apparatus. Moreover this apparatus contains many rotatable operating parts which require not only considerable expenses for seals, but also considerable energy consumption expenses. Generally the problems of effective soil cleaning methods are related to the properties of the soil, particularly to its widely variable grain size and especially with a somewhat high silt component, which leads quickly to stopping or clogging of the sieves, which is connected with increased wear of the mechanical parts contacting with it.